It is known that synchronisation is an essential procedure in a modern digital communication system. It is the procedure used by a remote unit (often referred to as User Equipment, UB, in UMTS or Customer Premises Equipment, CPE) to identify valid transmissions from infrastructure equipment (often referred to as Node Bs in UMTS) and align the remote frequency reference and timing to that used by the infrastructure.
UMTS Terrestrial Radio Access (UTRA) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) modes both provide a synchronisation channel (SCH) that is used by the UE to search for valid signals and perform the synchronisation procedure. The SCH transmission consists of one real valued Primary Synchronisation Code (PSC) and three complex Secondary Synchronisation Codes (SSC), all of length 256 chips. The PSC is common for all Node Bs, but the SSCs are Node B specific The PSC and SSC are transmitted simultaneously from a given Node B at a specific fixed time offset (toffset) from the start of time slot 0. The time offset is included to prevent the Interface (described in the 3G TS 25.xxx series of specifications).
A plurality of subscriber terminals (or user equipment (UE) in UMTS nomenclature) 112, 114, 116 communicate over radio links 118, 119, 120 with a plurality of base transceiver stations, referred to under UMTS terminology as Node-Bs, 122, 124, 126, 128, 130, 132. The system comprises many other UEs and Node Bs, which for clarity purposes are not shown.
The wireless communication system, sometimes referred to as a Network Operator's Network Domain, is connected to an external network 134, for example the Internet. The Network Operator's Network Domain includes:
(i) A core network, namely at least one Gateway GPRS Support Node (GGSN) 144 and or at least one Serving GPRS Support Nodes (SGSN); and
(ii) An access network, namely:                (ai) a GPRS (or UMTS) Radio network controller (RNC) 136-140; or        (aii) Base Site Controller (BSC) in a GSM system and/or        (bi) a GPRS (or UMTS) Node B 122-132; or        (bii) a Base Transceiver Station (BTS) in a GSM system.        
The GGSN/SGSN 144 is responsible for GPRS (or UMTS) interfacing with a Public Switched Data Network (PSDN) such as the Internet 134 or a Public Switched Telephone Network (PSTN) 134. A SGSN 144 performs a routing and tunnelling function for traffic within say, a GPRS core network, whilst a GGSN 144 links to external
However, the above known fixed initial rate negotiation scheme and the other possible schemes have the disadvantage that they are inefficient.
A need therefore exists for a synchronisation scheme for multi-rate communication wherein the abovementioned disadvantage may be alleviated.